The present invention relates to a cleaning device for a transfer belt which is constructed so as to transfer a toner image formed on the surface of a photosensitive member to a copy sheet while transporting the copy sheet in an image forming apparatus such as a copying machine and a printer.
There have been known conventionally image forming apparatuses such as copying machines and printers having a so-called transfer belt made of elastic material. This transfer belt transports a copy sheet fed through a pair of registration rollers from a cassette to a photosensitive drum. The transfer belt, to which a voltage of a specified level is applied, causes a toner image developed by a developing device and formed on the surface of the photosensitive drum to be transferred to the copy sheet, and then transports the copy sheet to a fixing device.
In the above apparatus, toner attached electrostatically to the surface of the photosensitive drum and that from the developing device may fly away and attach to the surface of the transfer belt. This causes the photosensitive drum and the rear face of the copy sheet to be stained. In view of this problem, the apparatus is provided with a cleaning device including a cleaning blade which is brought into pressing contact with the surface of the transfer belt to scratch off the attached toner. As a cleaning device employing a cleaning blade as mentioned above, there are in general two types: a counter type and a trail type. In the counter type cleaning device, as shown in FIG. 8, a cleaning blade 53 is disposed tiltingly such that a leading end thereof is in pressing contact with the surface of a transfer belt 50 at the bottom of the circumferential surface of a drive roller 51 for rotating the transfer belt 50 and is located backward relative to a base end thereof with respect to a rotating direction of the transfer belt 50 (a direction of arrow in FIG. 8).
In a trail type cleaning device, as shown in FIG. 9, a cleaning blade 54 is disposed tiltingly such that a leading end thereof is in pressing contact with the surface of a transfer belt 50 at a position of a placing member 55 disposed between the drive roller 51 and a driven roller 52 where the transfer belt 50 is stretched and is located forward relative to a base end thereof with respect to the rotating direction of the transfer belt 50 (a direction of arrow in FIG. 9).
In the above cleaning devices, the leading ends of the cleaning blades 53, 54 are fabricated to have an edge of a desired angle, e.g., right angle, with high accuracy. Thus, a mounting angle is important in bringing the cleaning blades in pressing contact with the transfer belt 50. In other words, an optimal cleaning function cannot be obtained in the case where the cleaning blades 53, 54 are not mounted at an appropriate angle with respect to the transfer belt 50. Accordingly, when the cleaning blades 53, 54 are pressed against the transfer belt 50 with a large force, the transfer belt 50 warps and consequently the cleaning blades cannot be pressed against the transfer belt 50 at the appropriate angle. In consideration of this disadvantage, as shown in FIGS. 6 and 7, the cleaning blade 53 is disposed in pressing contact with the transfer belt 50 at the circumferential surface of the drive roller 51 or the placing member 55 is disposed in a position opposed to the cleaning blade 54 through the transfer belt 50. In this way, it has been necessary to mount the cleaning blades 53, 54 in pressing contact with the transfer belt 50 while adjusting suitably the relationship between the pressing forces of the cleaning blades 53, 54 against the transfer belt 50 and the warping of the transfer belt 50 caused by these pressing forces.
However, if the cleaning blades 53, 54 are mounted in pressing contact with the transfer belt 50 using the drive roller 51 or the placing member 55, the transfer belt is held between the cleaning blades 53, 54 and the drive roller 51 or the placing member 55 and thereby a torque of the transfer belt 50 increases. The increased torque of the transfer belt 50 causes undesirably the slipping between the transfer belt 50 and the drive roller 51. This is extremely disadvantageous in terms of a sheet transporting performance, an image transferring timing, etc.